Creating hash: Key is unique string in array element, value is number of times it appears

putmant has asked for the wisdom of the Perl Monks concerning the following question:

I am new to Perl. I have created an array of the lines in my file (split on the white space. I want to exclude the query line. I am interested in element 2 (which is a string ie Streptococcus). I want to create a hash where a new key is created each time a novel string appears and the value will be 1. Each time it sees a string that has already been seen, I want to add 1 to the value of that key. My code returns a new key for every line with the value 2...What am I doing wrong? Thanks

 
#Example data:
#Query= 16sV5:44:FC62N5DAAXX:7:1:18808:1248 1:N:0:
#1111599 AB563244.1 Streptococcus macedonicus str. W28                
#1111215 AB563262.1 Streptococcus equinus str. MTS6
#repeats thousands of times...

while (my $line = <IN>) {
   chomp $line;


   if ($line =~ /Query=/) {

   } else{
   my @hit = split (/\s/, $line);
   my %genus = ($hit[2] , 1) ;

   if (exists ( $genus {$hit[2]})) {   
       $genus{$hit[2]}++;                 
   }   else{                                        
           $genus{$hit[2]} = 1;           
       }
            my @keys = keys %genus;
            my @values = values %genus;
            print "@keys\n@values\n";
   }
   next;
}
[download]

Comment on Creating hash: Key is unique string in array element, value is number of times it appears Download Code

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Re: Creating hash: Key is unique string in array element, value is number of times it appears by toolic (Bishop) on Oct 25, 2011 at 23:51 UTC
If you want to accumulate all your data into one hash, you need to declare it outside the while loop: `use warnings; use strict; use Data::Dumper; my %genus; while ( my $line = <DATA> ) { chomp $line; next if $line =~ /Query=/; my @hit = split( /\s/, $line ); $genus{ $hit[2] }++; } print Dumper(\%genus); __DATA__ Query= 16sV5:44:FC62N5DAAXX:7:1:18808:1248 1:N:0: 1111599 AB563244.1 Streptococcus macedonicus str. W28 1111215 AB563262.1 Streptococcus equinus str. MTS6` [download] prints... `$VAR1 = { 'Streptococcus' => 2 };` [download]	[reply] [d/l] [select]
Re^2: Creating hash: Key is unique string in array element, value is number of times it appears by putmant (Initiate) on Oct 26, 2011 at 17:26 UTC
Thank you so much! This worked perfect. Thanks to the other repilers as well	[reply]
Re: Creating hash: Key is unique string in array element, value is number of times it appears by spazm (Monk) on Oct 26, 2011 at 01:14 UTC
In perl, explicit code like this is not necessary as it would be in something more verbose like java or python. Perl has a concept of autovivification, where new values burst into being when needed. Also, ++ on a false value will return 1. In the case where `$hit[2]` is not a key in `%genus`, requesting the key will create a corresponding value of `undef`. Incrementing this value will return `1`. so this snippet: `#old snippet if (exists ( $genus {$hit[2]})) { $genus{$hit[2]}++; } else{ $genus{$hit[2]} = 1; }` [download] can be reduced to this snippet: `#new snippet $genus{ $hit[2] }++` [download] Example: `%genus = { } ; #genus is empty $genus{ foo }; #requests foo entry, and throws away. #genus is now { foo => undef } $genus{ foo } ++; # genus is now { foo => 1 }` [download] http://en.wikipedia.org/wiki/Autovivification	[reply] [d/l] [select]
Re^2: Creating hash: Key is unique string in array element, value is number of times it appears by johngg (Canon) on Oct 26, 2011 at 11:06 UTC
`%genus = { } ; #genus is empty` Let's try that! `knoppix@Microknoppix:~$ perl -Mstrict -wE 'my %genus = {};' Reference found where even-sized list expected at -e line 1. knoppix@Microknoppix:~$` [download] You probably meant to use parentheses rather than curly braces, which construct a reference to an anonymous hash. `knoppix@Microknoppix:~$ perl -Mstrict -wE 'my %genus = ();' knoppix@Microknoppix:~$` [download] I hope this is helpful. Cheers, JohnGG	[reply] [d/l] [select]
Re: Creating hash: Key is unique string in array element, value is number of times it appears by Khen1950fx (Canon) on Oct 26, 2011 at 02:54 UTC
I would try something more like this: #!/usr/bin/perl use strict; use warnings; use Data::Dumper::Concise; my(@array) = qw( 1111599 AB563244.1 Streptococcus macedonicus str. W28 + 1111215 AB563262.1 Streptococcus equinus str. MTS6 ); print Dumper( "Occur twice: @{numbers(\@array, 2);}" ); sub numbers { my ($newArray, $n) = (shift @_, shift @_); my(%count)= (); my(@temp_arr) = grep( {$count{$_} == $n;} grep ({++$count{$_} == 1;} @$newArray)); print "\%count:\n"; while ( my ($key, $value) = each(%count) ) { print Dumper( "$key => $value" ); } return \@temp_arr; } [download]	[reply] [d/l]